The EU AI Act's Prohibited AI Practices, which came into effect in February 2025, prohibits the use of AI systems for the purpose of inferring the emotions of natural persons in the workplace and in educational institutions. The specific details of the regulation are clarified in the Guidelines for Prohibited AI Practices. On the other hand, in Japan, there are no clear guidelines or regulations on emotion inference technology, and there have been some examples of demonstration experiments and introduction of such technology into products and services. In this paper, I examine how the protection of personal information should be handled in emotion inference technology. This paper clarifies that the regulations in the EU suggest the necessity of careful institutional design in Japan as well, taking into account the purpose of use, technical limitations, and the relationship with inner freedom.